Optimal Coordination of Ultrafast Solid-State Circuit Breakers in DC Microgrids

Abstract

Solid state circuit breakers (SSCBs) present ultrafast response time in interrupting short circuit fault currents in DC systems. Coordination of SSCBs is presented in this paper to minimize the isolation time, enhancing the reliabity, and obtain selectivity. Inverse time current characteristics (ITCC) are considered to describe the time-current trip curves of SSCBs. Three operating profiles are included named as overload, short circuit, and instantaneous regimes. In overload profile, thermal capability of the SSCBs is considered in determining the tripping time; whereas, operating speed is the deciding factor in short circuit and instantaneous profiles. A coordination time interval (CTI) is applied between primary and backup SSCBs to provide selectivity without the need of any communication link. To verify the correctness of the protective scheme, a 400V grid-connected DC microgrid including ultrafast MOV-RCD based SSCBs is simulated in LTspice.